Paint circle with Python in 3D view direction
Okay guys got it, sorry to again answer my own question:-)

rv3d      = context.space_data.region_3d
view_rot  = rv3d.view_rotation

segments = 32
mul = (1.0 / (segments - 1)) * (pi * 2)
points = [(sin(i * mul) * self._radius, cos(i * mul) * self._radius, 0) 
for i in range(segments)]

self._vertices = [view_rot @ mathutils.Vector(point) + 
                  self._center for point in points]